When liner is run through casing the means of support for the liner off the casing is the liner hanger. Traditionally the early liner hangers were held in a retracted position by one or more shear pins to prevent premature setting. Once the target location was reached for the liner hanger near the lower end of the casing the shear pins were broken and the liner hanger was set. Such designs cannot be reset at the same or a different location in the well.
Hydraulically set hangers have been developed that deploy slips radially outwardly when internal pressure is built up on a dropped ball. The internal pressure acts against a bias force on each slip toward the retracted position. The set is accomplished by internal pressurization to extend the slips against a bias force coupled with setting down weight on the mandrel with the slips extended. The weight of the assembly on the extended slips that bite against the surrounding casing would then hold the set. A pickup force that took the weight off the slips allowed the springs to retract the slips so that the liner and the associated hanger could be repositioned to be re-hung at another location with a subsequent deployment of the hanger. The slips are dogs that extend through mandrel openings as shown in US Publication 20090090508. The mandrel wall openings present leak paths around each piston 99 shown in FIGS. 7-9. If the weight is set down before full extension then the small connecting rod 101 can be bent and the dogs 97 may not retract. The limited bearing area for the dogs on the mandrel also limits the loading on the liner hanger.
Other resettable liner hangers are mechanical and generally operate with a j-slot mechanism that requires a combination movement of axial and rotational movement to set and a reversal of such movements to release. In deviated wellbores such movements may be problematic or if the running string is very long or for example coiled tubing then the rotational movements may be difficult to accomplish. Some examples of such designs are U.S. Pat. Nos. 4,496,000; 4,489,781; 4,010,804; 4,712,614 and 3,608,634.
The present invention provides a locking system for a resettable liner hanger that uses collets to prevent accidental setting during run in if the external housing is bumped against a downhole component. It sets hydraulically with a piston to move the collet assembly from the run in to the set position. The movement of the collet assembly compresses a return spring and moves an outer housing to ramp the slips out to the surrounding casing. Setting down weight with the slips extended holds the outer assembly in position against spring force. Picking up allows the spring to return the collet to a mandrel groove, resuming the run in position. These and other features of the present invention will be more apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.